Effect of grain boundary segregation on thermal conductivity of hot-pressed silicon carbide

In hot-pressed SiC with a sintering additive, Al2O3, the correlation between thermal conductivity at room temperature and phonon scattering by lattice defects (grain boundaries and point defects) was investigated. It is verified by both calculation within the Debye phonon model and experimental results that the principal scattering mechanism was determined to be grain boundary scattering.High-resolution transmission electron micrographs showed no thin secondary phase at the grain boundary interface. EDS line scans using a 3 nm probe showed the segregation of both Al and O atoms to grain boundaries. This grain boundary segregation leads to a concentration of defects and the formation of a disordered region at grain boundaries. We concluded that the thermal conductivity was decreased mainly by grain boundary scattering due to grain boundary segregation. The thermal conductivity is improved from ∼ 120 to 235 W/mK by decreasing the grain boundary concentration of both Al and O.